Binocular tubes of the Applicant are known in which the pupil distance adjustment is accomplished via two spindle drives, one of which is provided for each eyepiece carrier. This spindle drive can be added on at a later time and, for that reason among others, exhibits play. A hysteresis consequently occurs, so that upon adjustment of the pupil distance there is at first no reaction on the part of the adjustment device (correlation is not linear).
A further disadvantage with known pupil distance adjustment devices is the complexity of installation at a later time, larger physical volume, and high parts cost. Readoff accuracy is decreased because of the play and other factors (such as conversion ratio) in the spindle drive.
It is therefore desirable to describe an apparatus for pupil distance adjustment that is technically and mechanically simple and of compact configuration, and ensures user-friendly operation with a readoff accuracy unaffected by play.